Movable ballast in a sailing vessel

ABSTRACT

An external adjustable ballast system for keeled sailboats comprising a weight that is designed for low hydrodynamic drag, mounted through a beam to a shaft running down the leading edge of the fin keel. Turning the shaft moves the weight to optimize hull trim, both fore/aft and athwart ships, for a particular point of sail. If the weight and beam are shaped as a lifting body and mounted to the shaft such that it pivots as it rotates to optimize angle of attack, the dynamic balancing component can allow for a lighter weight. Ballast weight and beam can be raised or lowered to optimize performance for expected wind conditions. The leading edge of the fin keel is a rotatable non spherical shaft. When rotated, the shaft creates an asymmetric cross section which improves hydrodynamic efficiency of the keel.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to sailing yachts, and moreparticularly to externally ballasted high performance sailing yachts.

2. Description of Related Art

Typically, external ballast is located at the lowest point on rigidlyfixed keels. The keel serves two functions—it supports the externalballast and it provides a high aspect lifting surface to keep the vesselfrom sliding sideways as it sails upwind. As the vessel heels, theballast works to counteract the force of the wind. There is no restoringforce until some angle of heel is generated. As vessels heel, theeffective area of the lifting surface reduces, comprising the windwardperformance. Attempts to reduce the angle of heel, center on movingballast. Two typical methods of moving ballast to the windward side ofthe vessel include the swing keel and internal water ballast. The swingkeel mounts ballast on the bottom of the keel, using the keel as amoment arm to increase the effectiveness of the weight in generating arighting moment. Water ballast using pumps to fill bladders inside thehull as needed to adjust trim. Since the water is inside the hull themoment arm to the center of buoyancy is short, requiring significantlymore weight to an equivalent righting moment.

U.S. Pat. Nos. 5,163,377 and 5,622,130 describe various aspects of akeel-less sailing yacht that has fore and aft cambered foils for leewaycontrol and a dynamic gravitational ballast for heeling resistance. Aballast-supporting structure, in the form of an elongated strutextending downwardly from the hull, supports the ballast generallybeneath the hull. Twin fore and aft rotatable foils are also supportedby the hull with extension below the hull for optimum performance undera wide range of operating conditions, preferably being controlled by ahydraulic or electric system.

A keel-less sailing yacht with appendages in the form of a movableballast-supporting strut and twin fore and aft foils is sometimesreferred to as a canting ballast twin foil (CBTF) sailing yacht. SuchCBTF sailing yachts enjoy recognized sailing success accompanied bysignificant interest in CBTF technology. However, various structural andoperational concerns need attention.

For example, the downwardly depending foils and ballast-supporting struthinder operations in shallower water. In addition, replacement of foilsdamaged by vessel grounding is impaired. Furthermore, operatingperformance of larger sailing yachts, including those designed for oceanracing or cruising, can suffer somewhat under various sailing conditions(e.g., sailing off wind) due to the friction drag introduced by thedownwardly depending appendages. Thus, a need exists for CBTFimprovements in these respects.

U.S. Pat. No. 6,886,481 describes a pivotable deployable bulb mountedfoil apparatus for a sailboat whose foils can be deployed from a nestedposition and pivoted when needed for lateral resistance. This inventionis especially adapted to a canting keel where the sailboat loses itslateral resistance from the keel when the keel is canted.

SUMMARY OF THE INVENTION

Attempts to reduce the angle of heel center on moving ballast. Twotypical methods of moving ballast to the windward side of the vesselinclude: the swing keel and internal water ballast. This inventiondiffers from prior art in several ways. The examples cited above eitheradd weight, increases drag, or reduces the effective area of the liftingsurface of the keel. This invention maintains the vertical orientationof the keel to the hull as a lifting surface and does not add weight tothe vessel to increase the righting moment.

Water ballast systems require pumps and a water source to pump waterfrom one side of the hull to the other to increase the righting momentand decrease the angle of heel. Since the effectiveness of ballast isproportional to the distance of the ballast from the centerline of thevessel, and since water ballast by definition must be contained withinbladders or tanks mounted inside the ship's hull, significantly morewater weight is needed to generate the same amount of righting moment asballast suspended from the ship's keel. Mounting water ballast tanks andassociated plumbing in a ship uses significant space and the additionalweight affects sailing performance in several ways. The additionalweight increases the wetted area of the hull (the boat rides deeper thanit would with less weight), increasing drag and reducing performance.Shifting large quantities of water requires complex plumbing andmechanical equipment, and can include sensors and controls. Failures inany of these components can reduce the ships ability to move water tothe appropriate location, affecting the sailing performance and possiblyaffecting the safety of the vessel.

Another method of increasing the righting moment is to mount ballast onthe bottom of the ship's keel and hinge the keel on an axis longitudinalto the vessel centerline. This approach is commonly called a “swingkeel” as the keel can be “swung” outward to lifts the ballast andtherefore reduce the angle of heel. Because of the cost and complexityof this approach, most vessels employing this design are built forsailing competition. The swing keel approach adds no additional ballastweight, but swinging the keel away from the centerline of the boat hasseveral adverse affects. First, swinging the keel away from aperpendicular presentation reduces the aspect of the keel, allowing moreleeway when sailing upwind. Since this approach requires that theballast be raised as it is swung to one side, hydraulics are oftenemployed to perform this work. The structure of the hull therefore, mustbe designed to mount the keel hinge and control hydraulics and react thesubstantial forces generated when the ballast is lifted. Allowing thekeel to swing outwards requires that the hull also have a large openingfor the keel to mount with sufficient space for it to move to the fullextent of its travel. This opening, through which the keel is mounted,is sealed with a flexible membrane. This seal requires routineinspection and maintenance, requiring the boat to be regularly drydocked. In addition, if any component in the system fails, the vesselwould become unsafe and forced to retire from competition.

FIG. 1 and FIG. 2 show the overall concept of the rotating externallyballasted keel. The center of mass of the ballast is located aft of theshaft which supports the load and allows the ballast to rotate. Theconcept allows for a simpler and stronger and more reliableimplementation as compared to prior art.

In the preferred embodiment, the ballast is cantilevered from a rotatingshaft, no technical work is done to move the ballast (the ballast is notlifted—but rotated), decreasing structural and mechanism complexity.This approach eliminates the need for the complex hydraulics requiredfor swing keels and allowing the device to be manipulated by hand.Rotating seals on the shaft are much more reliable and easy to implementthan sealing the hinged area between a swing keel and hull. In thisapproach, even if the seals failed, the opening in the hull for theshaft could be made above the waterline, which would not allow water toenter the vessel—even if the seal completely failed, a safer approach.This design also provides for a clean transition from the hull to thekeel as compared to the flexible interface in a swing keel design,thereby avoiding the increase in drag associated with that flexible sealapproach.

The shaft is rotated by the crew from inside the vessel by using amoment arm attached to the shaft. The arm could be actuated manually orautomatically. The position of the arm would also indicate the positionof the ballast. The arm would be positioned approximately perpendicularto the boom. As the point of sail moved forward, the ballast would berotated to offset the force generated by the pressure on the sail. Thisadjusts both the fore/aft and athwart ships hull trim. FIG. 3 shows thetypical position of the ballast for different points of sail. Typically,crew position (“live ballast”) is moved to maintain fore/aft hull trim.The support shaft could also be angled back to cause the beam supportingthe ballast to produce hydrodynamic lift to further increase therighting moment. The more the ballast is rotated, the more the angle ofattack of the ballast beam would increase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a rotate-able ballast system for asailing yacht constructed in accordance with the present invention

FIG. 2 includes stern-on views of the location of ballast in theinstances of PORT TACK (2A) RUNNING DOWNWIND (2B) AND STARBOARD TACK(2C)

FIG. 3 includes plan views of appropriate locations of the ballast withrespect to sail positions in the sailing conditions of RUNNING DOWNWIND(3A), BEAM REACH (3B), and sailing UP WIND (3C)

FIG. 4 a shows an embodiment which includes axial extension of theballast to increase righting moment. Ballast can be extended by movingthe shaft axially, still allowing the shaft to rotate. FIG. 4 b includesan alternate vertical shaft mounting detail.

FIG. 5 Mounting details for an alternate embodiment showing shaftlocated in front of keel and mounting beam and ballast attachment

FIG. 6 show typical methods for shaft rotation and extension.

The following definitions are used herein to describe the hull geometry:

A centerline is a line lying in the vertical longitudinal plane cuttingthe hull down the middle from bow to stern.

Waterlines (or level lines) are defined as the intersection with thehull of waterplanes perpendicular to the hull centerplane, at variouselevations.

Sections are defined as the intersection of a series of spaced verticalplanes cutting the hull transversely to a centerline.

A midsection is one of the sections lying generally in the middle of thehull.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a typical hull 10 with fixed keel 11 and ballast 12. Theballast is mounted to shaft 13 which is mounted and supported in theforward portion of the fixed keel. Rotating shaft rotates the ballastaway from the centerline of the vessel. The connection and support ofthe ballast on the bottom of the keel can be arranged so that the centerof mass of the ballast moves forward and angles down when rotated.

FIG. 2 shows stern on views of the location of the center of mass ofballast 16 with respect to the centerline of the vessel 14 as it isrotated about the keel 15. In this alternate embodiment the ballast issimply supported on the shaft, allowing the center of mass to moveforward as the shaft is rotated, but in this embodiment, the center ofmass remains in the same plane rather than angling down when rotated.

FIG. 3 shows plan views of the forces on a typical vessel equipped withrotate-able ballast in different wind and rigged conditions. FIG. 3Ashows the vessel moving in the direction of the wind 17. In thiscondition, the sails 19 are rigged to make full use of available wind,generating a force 21 in line with the vessel hull 20 direction. Forthis running condition, the center of mass of the ballast is in linewith the keel (not rotated). FIG. 3B shows a vessel heading in adirection perpendicular to wind direction 22. For this condition, thesails 24 are trimmed to catch and direct the available wind to generatethe force from sales 25 which has two force components and a moment onthe vessel hull 23. One component of the force from the sales acts tomove the vessel forward (in the direction of the hull) and a secondcomponent acts to push the vessel 23 in the direct of the wind 22. Themoment works to tip the boat about its longitudinal axis. The secondforce is countered by the keel which presents a surface which generatesdrag in proportion to the aspect of the surface perpendicular to theline of force. As the vessel heels (rotates about it's centerline), theaspect ratio decreases, and the resistance to movement in the directionof the wind decreases. It is advantageous, therefore to minimize heel tomaintain forward momentum and minimize sliding sideways in the directionof the wind. The moment which acts to heel the vessel is counteracted bythe ballast 26. The mass of the ballast mounted below the keel generatesa moment equal to the mass times the distance of the mass from thecenter of buoyancy of the vessel. In the case depicted in FIG. 3A, thecenter of mass is aft of the center of buoyancy of the vessel, whichhelps counter the moment generated by the sails 21 which would act todrive the bow of the vessel 18 down. In the case depicted in FIG. 3B,the righting force can be maximized by rotating the ballast to act inline with the force from the sails 25. FIG. 3C depicts a vessel 28moving in the general direction of the oncoming wind 27. The sails 29are appropriately depicted for this running condition, generating theforce from the sails in the direction shown 30. For this runningcondition, the heeling moment is countered by the ballast 31 mosteffectively by locating the ballast 31 in the line of direction of forcefrom the sails 30. In the cases depicted in FIG. 3B and FIG. 3C, thereis a force component that attempts to push the vessel sideways that mustbe reacted by the keel. This is done most efficiently by maximizing theaspect ratio which reduces as the vessel heels. Therefore the vesselwill be most efficient when the ballast can be rotated to act in linewith the direct of the force from the sails.

FIG. 4 a depicts an embodiment where the ballast beam 33 is mounted tothe pivot shaft 13 on one end, and which supports the ballast 34cantilevered from the shaft. The shaft can be moved axially, moving theballast further from the center of buoyancy of the ship which in turnincreases it's righting moment. FIG. 4 b shows an alternate verticalmounting of the pivot shaft 32, such mounting also allowing the beam andballast to pivot and move axially with respect to the keel 11. In eachof the embodiments shown (the vertically oriented shaft and thenon-vertically oriented shaft, the beam and ballast are mounted to theshaft such that when the shaft is rotated, the beam and ballast sweepout a plan that is not horizontal and parallel to the bottom of theboat. In this configuration, the center of mass of the ballast actuallymoves forward and down with respect to it's normal centered position.This movement adds additional length to the moment arm between the shaftand the center of buoyancy of the vessel, increasing righting moment.Further, the movement of the ballast out of the shadow of the keel andinto the water flowing adjacent to the keel adds a hydrodynamic forcewhich is additive to the weight to further increase righting moment.These additional forces allow the vessel to be designed with a lowerballast weight than would otherwise be necessary, the lessened weightdecreases displacement and drag and further increases performance. It isobvious to one skilled in the art that it is also possible to mount theballast to the shaft such that it sweeps out a plane that is horizontal(parallel to the bottom of the hull).

FIG. 5 depicts an embodiment where the pivot shaft 35 is mounted on theleading edge of the keel 11, and the shaft where exposed to the waterhas a hydrodynamically efficient shape. The shaft is mounted at theupper and lower end of the keel, allowing it to pivot, and seals 36 areprovided to reduce drag as the shaft pivots. Pivoting the shaftconfigured as described modifies the hydrodynamic efficiency of thekeel. Two alternate embodiments are shown, but many variations arepossible to one skilled in the art.

FIG. 6 a shows an elevation view of one possible embodiment for manuallyrotating and extending the shaft. A handle 39 is mounted to the pivotshaft 37 through a pin 40. The shaft is secured in a housing 38 whichhas a series of radial slots 43 on its upper surface into which thehandle can fit, securing the handle from rotation. A pinion gear 42,mounted to the housing can be turned via a crank (not shown). A rackgear 41, machined into or mounted upon the upper end of the pivot shaft37 is acted upon by the pinion gear to axially move the shaft whichsupports the ballast under the keel. For embodiments which include theability to move the shaft vertically, the shaft vertical movement can becontrolled via the aforementioned rack and pinion, radial motioncontrolled via the handle and slot arrangement previously described—theradial motion transferred through a spline (not shown) acting in thecenter of the pivot shaft 37. Locking pins (not shown) would preventover travel of the vertical motion of the shaft. FIG. 6 b shows a planview of the handle 39 in relation to the shaft 37 and the housing 38.The radial slots 43 are best seen in this view. A variation to the slotdesign would be to incorporate a spring loaded dog or pawl that wouldact between the housing 38 and the shaft 37 (not shown) anywhere that itwould be conveniently accessible to the sailor. One skilled in the artcan devise a number of variations of manual control of the shaft andtherefore the ballast for this invention, and it would be simple to oneskilled in the art to replace or supplement the manual controls throughuse of gear motors and other powered devices.

Thus the invention allows for the design of a sailing yacht whichenhances the effectiveness of a fixed ballast, which can then bedesigned for minimum weight and maximum performance. Further, theinvention eliminates many of the drawbacks of prior inventions,including replacing the complex seals required by swing keels by simplerotary seals, eliminating much of the structure, cost and complexity andimproving the safety of vessel as compared to a swing keel design. Nofailure of any element of this design would risk the integrity of thevessel. The embodiments described here do so to illustrate the conceptsclaimed in the invention and do not purport to be the only embodimentspossible. Rather, one skilled in the art can envision a variety ofadditional ways to implement means to rotate and axially position afixed ballast as to maximize performance of a sailing yacht.

1-5. (canceled)
 6. A sailing yacht as recited in claim 16, wherein saidmounting of shaft, includes means for axially moving said rotate-ablymounted shaft in a vertical direction, allowing the ballast weight to beraised and lowered. 7-15. (canceled)
 16. A sailing yacht comprising: ahull with a fixed fin keel; said keel having a leading edge and atrailing edge; a shaft rotate-ably mounted on said leading edge of saidfin keel, said shaft having an upper and a lower end, said mounting ofshaft to include bearing support on said upper and said lower ends ofsaid shaft, said shaft having a central portion between said mountingsexposed to the water forward of said leading edge of said keel; a beamhaving a first end and a second end, said first end of said beam rigidlyfixed to said lower end of said shaft; a ballast weight mounted to saidsecond end of said beam; means connecting to upper end of said shaft forrotating said shaft such that when the said shaft is rotated, saidweight is moved in an arc about said shaft.
 17. A sailing yacht asrecited in claim 16 wherein the weight is shaped to have a lowcoefficient of hydrodynamic drag and has a center of mass.
 18. A sailingyacht as recited in claim 16 wherein the exposed central portion of theshaft has a non-circular cross section.
 19. A sailing yacht as describedin claim 18 wherein the central portion of the shaft is designed toblend with the leading edge of the keel and minimize hydrodynamic dragwhen in a non-rotated position.
 20. A sailing yacht as described inclaim 18 wherein rotating the shaft modifies the hydrodynamic efficiencyof the keel.
 21. A sailing yacht as recited in claim 17 wherein thecenter of mass moves forward and down with respect to the vessel.
 22. Asailing yacht as recited in claim 17 wherein the weight and beam whenrotated out of the neutral centered position act as a fin adding dynamicforce which acts to increase righting moment.
 23. A sailing yacht asdescribed in claim 16 further comprising means to secure the shaft andweight in any desired rotated position.
 24. A sailing yacht as describedin claim 23 wherein the means for securing the shaft from rotation is agear motor.
 25. A sailing yacht as described in claim 23 wherein themeans for securing the shaft from rotation is a lever resting in a slot.26. A sailing yacht as described in claim 23 wherein the means forsecuring the shaft from rotation is a pawl.
 27. A sailing yacht asdescribed in claim 16 wherein the means for rotating the shaft is a gearmotor.
 28. A sailing yacht as described in claim 16 wherein the meansfor rotating the shaft is a lever connected to the upper end of theshaft.
 29. A method of adjusting both fore/aft and athwart ships trimwhile under sail comprising: providing ballast rotate-ably mounted underthe keel and rotating said ballast beneath the keel.
 30. A method ofadjusting both fore/aft and athwart ships trim while under sailcomprising: providing ballast rotate-ably mounted under the keel,ballast also capable of being extended and retracted, and rotating andextending or retracting said ballast beneath the keel.